arXiv:physics/0403141 · Journal of the Optical Society of America B
Proposal for high-precision atomic-parity-violation measurements by amplification of the asymmetry by stimulated emission in a transverse electric and magnetic field pump-probe experiment
Amplification by stimulated emission of radiation provides an interesting means for increasing the sensitivity of atomic-parity-violation (APV) measurements in a pump-probe configuration well adapted to the 6S-7S Cs transition. It takes advantage of the large number of atoms excited along the path of the pump beam. In the longitudinal electric field configuration currently exploited in our ongoing APV measurement, this number is limited only by the total voltage sustainable by the Cs vapor. To overcome this limit we consider, both theoretically and experimentally, the possibility of performing the measurements in a transverse electric field configuration requiring a much lower voltage. We discuss the necessarily different nature of the observable and the magnetoelectric optical effects that come into play. These condition modifications of the experimental configuration with, in particular, the application of a transverse magnetic field. We suggest the possibility of rotating the transverse direction of the fields so as to suppress systematic effects. With a long interaction length a precision reaching 0.1% in a quantum-noise-limited measurement can be expected, limited only by the necessity of operating below the threshold of spontaneous superradiant emission of the excited medium. Were we to approach this limit, however, we could greatly amplify the asymmetry using triggered superradiance.
Amplification by stimulated emission of radiation provides an interesting means for increasing the sensitivity of atomic-parity-violation (APV) measurements in a pump-probe configuration well adapted to the 6S-7S Cs transition. It takes advantage of the large number of atoms excited along the path of the pump beam. In the longitudinal electric field configuration currently exploited in our ongoing APV measurement, this number is limited only by the total voltage sustainable by the Cs vapor. To overcome this limit we consider, both theoretically and experimentally, the possibility of performing the measurements in a transverse electric field configuration requiring a much lower voltage. We discuss the necessarily different nature of the observable and the magnetoelectric optical effects that come into play. These condition modifications of the experimental configuration with, in particular, the application of a transverse magnetic field. We suggest the possibility of rotating the transverse direction of the fields so as to suppress systematic effects. With a long interaction length a precision reaching 0.1% in a quantum-noise-limited measurement can be expected, limited only by the necessity of operating below the threshold of spontaneous superradiant emission of the excited medium. Were we to approach this limit, however, we could greatly amplify the asymmetry using triggered superradiance.
We detect atomic parity violation (APV) by using stimulated emission, in the form of a chiral optical gain of a cesium vapor on the 7S-6P3/2 probe transition, consecutive to linearly polarized 6S-7S excitation. The method relies on a pump-probe scheme in which the excited 7S state is populated, in zero magnetic field, by an intense, pulsed excitation beam, with a linear polarization [epsilon]ex and a wave vector [k] parallel to the applied electric field [E]. The atoms are then probed by a second, collinear pulsed laser beam, tuned to resonance with the 7S - 6P3/2 transition. The probe beam is amplified by stimulated emission and its linear polarization [epsilon]pr undergoes a small change of direction, due to the presence of the pseudoscaler PV term in the gain. This dichroism, with axes at +/-45° from the ([epsilon]ex,[E]) plane of symmetry of the experiment, is smaller than the parity-conserving, Stark linear dichroism by the ratio of the Stark to the PV 6S-7S transition amplitudes [beta]E/ E1pv, approximately 10^6. As a result the gain axes are tilted by an angle [theta]pv = E1pv/[beta]E, approximately 1µradian.This is the relevant APV quantity, measured by balanced-mode, two channel polarimetry, with dedicated real-time calibration. This detection method has been validated by a measurement of expected sign and magnitude with a 9% accuracy [ref. 1], now improved by more than a factor of two, thanks essentially to a dichroic polarization-tilt magnifier [ref. 2]. Rotational symmetry around the common pump-probe beam axis is used to reduce systematic effects [ref. 3], among which the parity-conserving Jones dichroism due to transverse E and B fields. This latter kind of magneto-optical effects has already been observed in especially chosen liquids thanks to the application of intense (>10T) magnetic fields. Here, symmetry discrimination, applied to the strongly forbidden 6S-7S transition, allows its detection with applied magnetic fields 10^5 to 10^7 times weaker, in a dilute vapor, where the mechanisms involved are clearly understood [ref. 3]. Besides, we discuss a novel kind of magneto-optical effects manifesting parity violation, as possible observables for APV measurements to the 0.1% precision level on the 6S-7S Cs transition. They consist in observing a parity violating circular dichroism in the presence of transverse electric and magnetic fields [ref. 4]. The advantage, as compared to the longitudinal E field configuration, is that the interaction length can be made much longer without increasing the applied potentials. Thanks to the much larger optical density of the excited vapor, stimulated emission gives rise to considerable amplification of the polarimetric signal during the propagation of the probe beam. Even moderate transverse electric fields would allow to reach the triggered superradiance regime, for further enhancing the PV asymmetry. Finally we suggest a means of rotating the transverse direction of the fields so as to restore the cylindrical symmetry and to suppress systematic effects, as in the longitudinal E field configuration. [1] J. Guéna et al.: Phys. Rev. Lett. 90, 143001, (2003) [2] D. Chauvat et al.: Opt. Commun. 138, 249 (1997) [3] M.-A. Bouchiat, J. Guéna, M. Lintz: Eur Phys J D28, 331 (2004) [4] J. Guéna, M. Lintz & M.-A. Bouchiat: arXiv:physics/0403141 & JOSA B, to be published
A pump-probe atomic parity violation (APV) experiment performed in a longitudinal electric field, provides a signal breaking mirror symmetry while preserving the cylindrical symmetry of the set-up. The excited vapor acts on the probe beam as a linear dichroic amplifier, imprinting a very specific signature on the detected signal. Our differential polarimeter is oriented to yield a null result unless the excited atoms are endowed with a chirality of some kind. Ideally, only the APV (E-odd) and the calibration (E-even) signals contribute to a chiral atomic response, a situation highly favourable to the detection of a tiny effect. In the present work we give a thorough analysis of possible unwanted defects like stray transverse fields or misalignments which would spoil the ideal set-up and lead to chiral systematics. A possible way to suppress such effects is to perform global rotations of the experiment by incremental steps of 45 degrees, leaving both stray fields and misalignments unaltered. The conspiration of at least two defects is necessary to affect the E-odd polarimeter signal. The transverse nature of the defects manifests itself by an azimuthal cosine square modulation. The harmful systematics are those which survive the averaging over four successive configurations. They require the presence of a stray transverse electric field, which can be determined and eventually minimized by auxiliary measurements of the systematic effects, amplified by applying a known external magnetic field. Transverse stray magnetic fields must be compensated by a similar procedure. We also propose statistical correlation tests as diagnoses of the aforementioned systematic effects.
This paper presents our experimental strategy for detecting an electric-field controlled pulsed-excited highly forbidden transition such as the 6S-7S transition of the Cs atom. The amplification of a pulsed probe beam close to resonance for one hfs component of the 7S – 6P3/2 transition is monitored. Furthermore the polarization modification experienced by the probe beam as a result of its interaction with the vapor is meticulously analysed. In convincing examples we point out the high sensitivity and complete selectivity of the method for the angular anisotropy of the 7S state, such as orientation or alignment created in the 6S-7S excitation process. We illustrate the flexibility of the method by varying the pump-probe delay, or by changing the relative positions of the beams or the magnitude of the E-field that directly controls the optical gain. A smooth transition from linear amplification to triggered superradiance is observed which necessitates readjustment of the probe intensity for optimal detection. We demonstrate the vapor-induced enhancement of the amplification anisotropy, expected at high optical density.
We have detected, by using stimulated emission, an atomic parity violation (APV) in the form of a chiral optical gain of a cesium vapor on the 7S-6P(3/2) transition, consecutive to linearly polarized 6S-7S excitation. We demonstrate the validity of this detection method of APV, by presenting a 9% accurate measurement of expected sign and magnitude. We stress several advantages of this new approach which fully exploits the cylindrical symmetry of the setup. Future measurements at the percent level will provide an important cross-check of an existing more precise result obtained by a different method.
A high-sensitivity optically pumped atomic magnetometer working in the geomagnetic range utilizing the light-narrowing effect and in-phase excitation is described. The setup is based on a simple pump–probe arrangement built around a Cs vapor cell whose active volume is 64 mm3. The transverse oscillating field is applied parallel to the probe beam to drive Zeeman resonance, and the in-phase component of the resonance signal is measured to determine the field. The sensitivity of the magnetometer is improved by pumping most atoms into the stretched state. Consequently, spin-exchange relaxation is suppressed, and a sensitivity of 0.1 pT/Hz1/2 in the range of 10 μT is achieved. This magnetometer has the advantages of large dynamic range, high performance of low-frequency stabilization, high response speed, and compact size. It can be used for many cutting-edge applications such as detection of magnetic anomalies.
We report the design and performance of a nonmagnetic drift stable optically pumped cesium magnetometer with a measured sensitivity of 35 fT at 200 s integration time and stability below 50 fT between 70 and 600 s. The sensor is based on the nonlinear magneto-optical rotation effect: in a Bell–Bloom configuration, a higher order polarization moment (alignment) of Cs atoms is created with a pump laser beam in an anti-relaxation coated Pyrex cell under vacuum, filled with Cs vapor at room temperature. The polarization plane of light passing through the cell is modulated due the precession of the atoms in an external magnetic field of 2.1 μT, used to optically determine the Larmor precession frequency. Operation is based on a sequence of optical pumping and observation of freely precessing spins at a repetition rate of 8 Hz. This free precession decay readout scheme separates optical pumping and probing and, thus, ensures a systematically highly clean measurement. Due to the residual offset of the sensor of <15 pT together with negligible crosstalk of adjacent sensors, this device is uniquely suitable for a variety of experiments in low-energy particle physics with extreme precision, here as a highly stable and systematically clean reference probe in search for time-reversal symmetry violating electric dipole moments.